The output signal from an incremental encoder is a square wave signal. This can be categorized into two types: an incremental encoder with a commutation signal and a standard incremental encoder. The latter typically features a two-phase orthogonal square wave, with pulse outputs labeled A and B, along with a zero-bit signal Z. In contrast, an incremental encoder with a commutation signal includes all these signals plus an additional electronic commutation signal UVW. These UVW signals differ by 120 degrees and correspond to the number of magnetic poles on the motor's rotor. Aligning the phases of the UVW electronic commutation signal with those of the incremental encoder with a commutation signal and the rotor poles—or the electrical angle—is essential. Here’s how it can be done:
1. Use a DC power source to apply a current less than the rated current to the motor’s DC windings, setting U in and V out to orient the motor shaft to its equilibrium position.
2. Utilize an oscilloscope to monitor the U-phase signal and the Z signal of the encoder.
3. Adjust the relative positions between the encoder shaft and the motor shaft.
4. During adjustment, keep observing the U-phase signal edge of the encoder and the Z signal until the Z signal stabilizes at a high level (assuming the default state of Z is low). At this point, lock the positional relationship between the encoder and the motor.
5. Manually reverse the motor shaft back and forth. If the motor shaft naturally returns to its equilibrium position after releasing your hand and the Z signal remains stable at a high level, the alignment is successful.
After disconnecting the DC power supply, further verification can be carried out:
1. Use an oscilloscope to observe the U-phase signal of the encoder and the back electromotive force (back-EMF) waveform of the motor’s UV phase.
2. As you rotate the motor shaft, the rising edge of the U-phase signal from the encoder should align with the zero-crossing point of the motor’s UV back-EMF, and the Z signal of the encoder should appear at this zero-crossing point.
This verification method can also serve as an alignment technique. It’s important to note that at this stage, the phase zero point of the U-phase signal of the incremental encoder aligns with the phase zero point of the motor’s UV back-EM potential. Given that the U electrode potential of the motor differs from the UV line back-EM potential by 30 degrees, this alignment means the phase zero point of the U-phase signal of the incremental encoder aligns with the -30-degree phase point of the opposite potential of the motor U. Consequently, the phase angle of the motor's electrical angle matches the phase of the potential waveform of the U opposite, ensuring that the phase zero of the U-phase signal of the device aligns with the -30-degree point of the motor's electrical phase angle.
Some servo companies prefer to directly align the zero point of the encoder’s U-phase signal with the zero point of the motor’s electrical angle. To achieve this:
1. Connect three resistors in a star configuration and link them to the UVW three-phase windings of the motor.
2. Use an oscilloscope to observe the midpoint of the U-phase input of the motor and the star-shaped resistor to approximate the U-potential waveform of the motor.
3. Adjust the relative position of the encoder shaft and the motor shaft, or the relative position of the encoder housing and the motor housing, based on operational convenience.
4. While adjusting, observe the rising edge of the U-phase signal of the encoder and the zero-crossing point of the opposite potential waveform of the motor U from low to high, making the rising edge and the zero-crossing point coincide. Lock the relative position relationship between the encoder and the motor to complete the alignment.
Since standard incremental encoders lack UVW phase information and Z signals can only reflect one point within a circle, there is no direct phase alignment potential for these encoders, so they won’t be discussed here.
Please note that this explanation is provided in English and may differ slightly from the original Chinese text.
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